Hydrocarbon oils having improved electrical properties



Patented Sept. 6, 1960 HYDROCARBON OILS HAVING IMPROVED ELECTRICALPROPERTIES John P. McDermott, Springfield, N.J., assignor to EssoResearch and Engineering Company, a corporation of Delaware No Drawing.Filed 'July 30, 1958, Ser. No. 751,848 9 Claims. (Cl. 52-45) The presentinvention relates to hydrocarbon oils havmg improved electricalproperties and more particularly relates to petroleum products such asturbo-jet engine fuels, naphthas, gasolines, kerosenes, heating oils,solvents and similar liquid hydrocarbons boiling in the range betweenabout 75 F. and about 750 F. to which have been added certain tetraalkylammonium salts of hydroxy carboxylic acids which greatly reduce thetendency of such oils to generate and accumulate electrical chargeswhich can liberate suflicient energy to ignite the hydrocarbon vapors inair during handling and storage.

Considerable attention has been focused in recent years upon theelectric properties of hydrocarbon oils as a result of explosions whichhave occurred during the handling of such oils. It has been establishedthat these explosions have probably been due to tribo-electricdischarges. Although most such explosions have taken place whileturbo-jet aircraft fuels were being transferred from one tank toanother, there have been instances of explosions occurring during thehandling of gasolines, kerosenes, solvents and other hydrocarbonproducts boiling between about 75 and about 750 F. when the ambienttemperatures were slightly above-the flash points of the products.Turbo-jet engine fuels are particularly hazardous because theirvolatility is such that their vapors form explosive mixtures with airover a relatively Wide temperature range.

The mechanisms involved in explosions of hydrocarbon oils attributed totribo-electricity are not fully understood; but it is believed thationic contaminants present in the hydrocarbons in very smallconcentrations play an important role. Studies have shown thatelectricity is rapidly generated when hydrocarbons containing smallamounts of materials capable of undergoing charge separation flow past asolid or liquid interface. Electrical potentials of several thousandvolts can readily be built up in this manner. When such a potentialreaches a sufficiently high level, electrical energy is discharged andmay ignite hydrocarbon vapors present in admixture with air to cause anexplosion. This is, of course, only one explanation of the phenomenonand there may be other mechanisms involved.

The contaminants in hydrocarbons which undergo charge separation asdescribed above influence the conductivity of the hydrocarbon stream.When the con-.

centration of materials capable of undergoing charge separation in thehydrocarbons is low, conductivity is low. As the concentration ofmaterials capable of undergoing charge separation increases,conductivity also increases. Since increased conductivity tends topermit .and accumulate electrical charges to a dangerous degree.

It has been suggested in the past that the danger of explosions ofhydrocarbons could be abated by adding .to the hydrocarbons certainpolyvalent metal soaps,

magnesium oleate and related metallic compounds, for example, whichwould increase the specific conductivity of the hydrocarbons to a valuegreater than about 1X10 mho/cm. Mixtures of such compounds have beensaid to be particularly effective. Although such additives do markedlyincrease the conductivity of hydrocarbons, it has been found that theirusefulness is generally limited to a very narrow concentration range. Ifthe concentration of such an additive in an oil is inadvertentlyreduced, there may be greater danger of an explosion than if no additivewere present at all. For this reason, the additives suggested for useheretofore have generally proved inadequate.

The present invention provides a new and improved class of additives foruse in hydrocarbon oils boiling in the range between about F. and about750 F. that afiords substantially greater protection against explosionsdue to tribe-electric discharges than compounds of the prior art. Inaccordance with the invention, it has been found that certain tetraalkylammonium salts of hydroxy carboxylic acids are surprisingly eifectivefor this purpose when added to turbo-jet engine fuels, gasolines,kerosenes, heating oils, solvents and similar hydrocarbon oil products.The additives of the invention markedly increase the specificconductivity of such products and furthermore, as shown hereinafter,decrease the amperage of streaming current and the number of highvoltage discharges which occur while the products are being pumped, evenwhen the additives are present in only extremely low concentrations. Theadditives employed in accordance with the invention are tet-raalkylammonium salts of hydroxy carboxylic acids containing from 2 to 10carbon atoms per molecule. Examples of such hydroxy carboxylic acidswhich may be employed in preparing the additives of the inventioninclude glycolic acid, lactic acid, hydracrylic acid, 3-hydroxybutyricacid, 2-hydroxybutyric acid, l-hydroxybutyric acid, glyceric acid,erythric acid, arabitic acid, mannitic acid, gluconic acid, galacturonicacid, tartronic acid, malic acid, tartaric acid, trihydroxyglutaricacid, saccharic acid, citric acid, mandelic acid, phenyl-lactic acid,tropic acid and gallic acid. The additives thus include tetraalkylammonium salts of both aliphatic and cyclic carboxylic acids containingfrom 2 to 10 carbon atoms per molecule. The acids must contain at leastone hydroxy group as well as one carboxyl group. They may, however,contain up to 5 hydroxyl groups and up to 4 carboxyl groups. Salts ofthe aliphatic hydroxy carboxylic acids containing from 2 to 6 carbonatoms per molecule are preferred. Tetraalkyl ammonium salts of malicacid and gluconic acid, wherein one hydroxyl group and one carboxylgroup are attached to a carbon atom in common, have been foundpreferred.

The tetraalkyl ammonium salts of the acids set forth in the precedingparagraph may readily be prepared by treating a quaternary ammoniumhydroxide with the desired hydroxy carboxylic acid and then removing thewater formed by means of an azeotropic distillation employing a solventsuch as benzene or toluene. Suitable tetraalkyl ammonium hydroxides foruse in this reaction are those having alkyl groups of from 1 to 24carbon atoms in length. Examples of such quaternary ammonium hydroxidesinclude tetrapropyl ammonium hydroxide, ethyl tributyl ammoniumhydroxide, butyltrihexyl ammonium hydroxide, dimethyl dihexadecylammonium hydroxide, tetraheptadecyl ammonium hydroxide and the like.Quaternary ammonium hydroxides prepared from naturally occurringmaterials such as coconut oil, tallow fat and soy bean oil are widelyavailable on the commercial market and are preferred. A typical mixtureof such commercial quaternary ammonium hydroxides is trimethyl soyaammonium hydroxide. The soya group is derived from soy bean oil and iscomposed of 8% C 91% C and 1% C alkyl chains. Similar mixtures 'arederived from Lorol alcohols, which are mixtures of primary alcoholscontaining from 10 to 18 carbon atoms prepared by the hydrogenation ofcoconut oil. Such mixtures are described in US. Patent No. 2,560,588.Quaternary ammonium hydroxides having 1 or more such mixed alkyl groupsmay be employed.

The tetraalkyl ammonium salts of hydroxy carboxylic acids describedabove are, in accordance with the invention, incorporated intohydrocarbon oils boiling in the range between 75 F. and about 750 F. inconcentrations ranging from about 0.00005% to about 0.5% by weight.Concentrations between about 0.0025 and about 0.05% are generallyeffective and are preferred.

The hydrocarbon oils in which the additive of the invention may beemployed are those boiling between about 75 and about 750 F.,particularly petroleum distillate fuels boiling in that range. Suchfuels include gasolines, aviation turbo-jet fuels, kerosenes, dieselfuels and heating oils. Gasolines as referred to herein are mixtures ofvolatile hydrocarbons boiling between about 75 F. and about 450 F. asdetermined by ASTM D-8656 and are defined by ASTM Specifications D9l0-56and D439-56T. Such gasolines may contain various beneficial additivessuch as anti-knock agents, scavenging agents, antioxidants, dyes,anti-icing agents and solvent oils in total additive concentrations upto about by weight. Aviation turbo-jet fuels comprise mixtures ofvolatile hydrocarbons boiling in the range between about 100 F. andabout 600 F. and are defined by US. Military Specifications MIL-F-5616,MIL-F- 5624C, MlLF25524A, and MIL-F-25558A. Diesel fuels as referred toin connection with the invention in general boil. between 250 F. and 750F. and are covered by ASTM Specification D97553T. Heating oils as theterm is used herein include both kerosenes and burner fuels fallingwithin grades 1 and 2 of ASTM Specification D39648T. As pointed outheretofore, the additives of the invention are particularly effective inturbo-jet aviation fuels. They may, however, also be employed insolvents, naphthas, transformer oils and other hydrocarbon oils boilingbetween about 75 F. and about 750 F.

The exact nature and objects of the invention may be fully understood byreferring to the following examples.

EXAMPLE 1 In order to determine the effectiveness of the addition agentsof the invention, the specific conductivities of samples of a turbo-jetaviation fuel containing various amounts of the additives weredetermined. The fuel employed was representative of the W4 fuels definedby US. .Military Specification MIL-F-5624C and had an API gravity of48.7, a Reid vapor pressure of 2.5

4 lbs/sq. in. and a to 520 F. boiling range. Specific conductivitieswere measured by applying a fixed direct current voltage to a Balsboughtype 2TN50 conductivity cell containing the sample. The cell wasconnected in series with an accurate standard high resistance. Currentflowing in the circuit was determined by measuring the voltage acrossthe standard resistance with a Keithley electrometer and applying Ohmslaw. Knowing the voltage drop across the conductivity cell and thecurrent flowing in the circuit, the resistance of the sample wascalculated. This resistance,'multiplied by the cell constant, gave thespecific resistance. The specific conductivity is the reciprocal of thespecific resistance and has the dimensions, mho/cm. The specificconductivity values thus obtained are shown in the following table.

Table l SPECIFIC CONDUCTIVITIES 0F FUELS CONTAINING QUATERNARY AMMONIUMSALTS OF HYDROXY OAR- BOXYLIC ACIDS Specific Fuel Conductivity mho/cm.

1 .l'P-4+No additive 6X10- 2 JP4+0.01 wt. percentMono-(Trlmethylsoyaammonium) malate 1.0)(10- 3 JP4+0.01 wt. percentDi-(Trimethylsoyaammonium) malate 1.9)(10' 4 JP4+0.01 wt. percentTrimethylsoyaammomum glycolate LOXIO- 6 JP4+0.01 wt. percentMono-(Trimethylsoyaammonium) tartrate 2. 4X10- 6 JP-4+0.01 wt. percentTrimethyls lactate 1. 5X10'" 7 JP-4-l-0.01 wt. percent Dimeth niumgallate 2.2X10" 8 J'P4+0.01 wt. percent Trimethylsoyaammoninm g8 ate1.6)(10' 9 IPA-+0.01 wt. percent Mono-(Trtmeth lsoyaammonium) citra 1.4X10- 10 JP4+0.005 wt. percent Dimethy monium gluconate 1. 4X10-" 11IPA-+0.01 wt. percent Trimethylsoyaammoninm gluconate 3.0X10- 12JP1+0.05 wt. percent Trimethylsoyaammonium gluconate 1.7X10' 13-.-JP-4+0.01 wt. percent Dimethyldisoyaammonium gluconate 3.1)(10QUATERNARY AMMONIUM SLATS OF STRAIGHT CARBOXYLIO ACIDS 14 JP4+0.01 wt.percent Di-(Dimethyldisoyaammonium) sebacate B.4 10-" 15 J P4+0.0l wt.percent Trimethylsoyaammom'um caproate v4.3)(10- From the above table itcan be seen that the additives of the invention increased the specificconductivity of the turbo-jet aviation fuel from the initial value ofSamples of a turbo-jet aviation fuel of the JP-4 type to which had beenadded quaternary ammonium salts of hydroxy carboxylic acids weresubjected to a labo ratory pumping test designed to demonstrate theeffectiveness of the additives in decreasing electrical discharges whenthe fuel was pumped over a solid having a large surface area. The testwas carried out by pumping the liquid through a glass tube containingglass wool as a charge separating surface and measuring during aten-minute interval the number of discharges across a calibrated sparkgap connected between the glass wool and ground. The liquid was pumpedfrom a reservoir through a rotameter and then passed downwardly througha one inch internal diameter glass pipe 15 inches 55 long, after whichit was returned to the reservoir. The glass pipe contained 3 grams ofCorning Pyrex Filtering Fiber glass wool which was wound around aremovable rack. The rack was made of glass rods and had cross pieces tosupport the glass wool. The pump was an Eastern Industries Centrifugalpump Model B-1 and the rotarneter Was a Brooks Tru Taper, #615-2. Theequipment Was joined with mm. internal diameter glass tubing having balljoints to facilitate dismantling. Half-inch Lucite was used for the baseand for the bracket which supported the glass pipe. A tungsten probe waspassed through the glass pipe to make contact with the lower portion ofthe glass wool. The probe was connected to an adjustable spark gap, theother side of the gap being grounded. The gap was adjusted to 0.064 sothat it would spark at 7,000 volts. Sparks across the gap were detectedby noting deflections of the pointer of a Keithley Model 200electrometer fitted with a Keithley Model 2005 detector, the latterplaced so that it pointed at the insulated side of the spark gap. Theentire apparatus was enclosed in a humidity cabinet constructed ofLucite.

Before each test, the unit was taken apart, washed with chloroform,dried with nitrogen and reassembled with a fresh hat of glass wool woundon the glass rack. Lucite parts were cleaned by washing with ethanol. A500 cc. sample of the fuel to be tested was placed in the reservoir, therelative humidity in the cabinet was adjusted to a value between and at70 F. by a stream of nitrogen, the pump motor was adjusted by means of aVariac to give a flow rate of 1500 cc. per minute as measured by therotameter and the number of 7000 kilovolt sparks produced during 10minutes of pumping was recorded. The data obtained in this manner,together with specific conductivity data obtained as described inExample 1, are set forth in Table II.

Table II EFFECTIVENESS OF ADDITIVES FOR REDUCING -ELEO- gglgll ALDISCHARGES IN THE LABORATORY PUMPING No. of 7 kv. Specific Con- FuelDischarges/ duetivity .TP-4 32 1. 2X10- .TP-4+0.005%Dimethyldisoyaarnmonium Gluconate 0 1. 3X10- .TP4+0.01% Dimethyldisoaarnmoniurn Gallate 0 1. 6 10- EXAMPLE 3 In order to aiford a comparisonbetween the eifectiveness of the additives of the invention andadditives proposed in the past for reducing the accumulation anddischarge of electricity in hydrocarbons, streaming cur-rent tests werecarried out on samples of a fuel containing varying amounts oftrimethylsoyaammonium malate and samples of the same fuel containing amixture of 61 parts of chromium dioctyl salicylate and 39 parts ofcalcium dioctyl sulfosuccinate. These tests were similar to the testdescribed in the preceding example except that the equipment wasmodified by substituting a stainless steel pipe for the glass pipepreviously used to hold the glass wool filter. This pipe was insulatedfrom the 6 receiving tank and was grounded. Streaming currents weremeasured with a Keithley micro-microammeter connected between the tankand ground. Data as to the specific conductivity and number of 7kilovolt discharges during a 10 minute interval as described in Examples1 and 2 were also obtained. The results of these tests are shown inTable III.

Table III COMPARISON OF THE EFFECTIVENESS OF ADDITIVES OF THE INVENTIONAND PRIOR ART ADDITIVES 1 Additive A-Mixtnre of 61 parts of chromiumdioctyl salicylate and 39 parts of calcium dioctyl suliosuccinate.

2 Additive BDimethyldisoyaammonium malate.

The data set forth in Table III above show that the additive of theinvention, the trimethylsoyaammonium malate, while less potent forincreasing specific conductivity than the additive of the prior art wasmuch more potent for decreasing the streaming current and the number ofhigh-voltage discharges, even when it was used in extremely lowconcentrations. It is evident that the decreasing of flow of current andof high voltage discharges under conditions of pumping is moreindicative of practical utility of the additives than an increase inconductivity measured under stationary conditions in a cell.

EXAMPLE 4 Further tests were carried out to determine the comparativeeffectiveness of the additives of the invention and other additives bypumping heating oil samples containing the various additives through aglass wool filter and a plastic pipe into the open top of a tank. Theheating oil employed had a 32 API gravity and a 347 to 660 F. boilingrange. Analyses showed that this heating oil contained traces ofasphaltic impurities.

The apparatus employed in the test comprised a 13 gallon tank to whichthe heating oil was pumped at a rate of 3 gallons per minute through theglass wool filter and a /2" diameter polyethylene pipe. The tank wallwas grounded. It was found that when this heating oil containing tracesof asphaltic impurities was pumped through the filter and pipe into thetank, a streaming current of 3X10 amperes was generated. The streamingpotential was 9000 volts per inch 3 inches from the glass Wool and thepotential between the tank and ground, when the tank was not grounded,built up to 40,000 volts. Brilliant discharges 8 to 10 inches in lengthoccurred repeatedly in the polyethylene pipe when a grounded probe wascontacted with the pipe. These localized discharges may constitute apronounced hazard in the handling of fuels, solvents and similarhydrocarbon oils.

Similar tests were then carried out using samples of the heating oilcontaining trimethylsoyaammonium gluconate, di-(trimethylsoyaammonium)malate, which are additives in accordance with the present invention,and those other additives which have been proposed by the prior art,namely calcium sulfonate, commercial additive D, and a mixture of theselast two. The localized discharges obtained with samples of the heatingoil containing each of these additives during a 10 minute period weremeasured. The results obtained are shown in Table IV.

7 Table IV LOCALIZED DISCHARGES WITH ADDITIVE BLENDS IN HEATING OILLocalized Discharges/10 Minute Period Di-(trimethylsoya ammonnium)Malate Calcium Sulfonate Mixed with Oommercial Additive Additive, Wt

percent Trimethylsoyaamm onium Gluconate Commercial Additive CalciumSulfonate The data set forth in Table IV demonstrate that thetrimethylsoyaammonium gluconate and the di-(trimethylsoyaammonium)malate, quaternary ammonium salts of hydroxy carboxylic acids are muchmore effective for reducing localized discharges than the calciumsulfonate, the Commercial Additive D or the mixture of the calciumsulfonate and the Commercial Additive D. No localized discharges at alloccurred with the samples containing the malate in concentrationsgreater than 0.0005 wt. percent. The gluconate was slightly lesseffective than the malate but was much better than the sulfonate and theCommercial Additive D alone or in combination.

It will be understood that the additives of the present invention may beincorporated into fuels, solvents and other hydrocarbon oils boiling inthe range between about 75 F. and 750 F. in conjunction with otheradditives intended to improve other properties of such oils. Such otheradditives include, for example, stabilizing agents, haze inhibitors,dyes, dye stabilizers, rust inhibitors and the like.

What is claimed is: p

1. A hydrocarbon oil boiling in the range between about F. and about 750F. having incorporated. therein from about 0.00005 to about 0.5% byweight of a tetraalkyl ammonium salt of a C to C unsubsti-' tutedhydroxy carboxylic acid, the alkyl groups of said salt each containingfrom 1 to about 24 carbon atoms.

2. An oil as defined by claim 1 wherein said salt is a tetraalkylammonium salt of a C to C aliphatic hydroxy carboxylic acid.

3. An oil as defined by claim 1 wherein said salt is present in aconcentration of from about 0.0025% to about 0.05% by weight. a

4. A liquid hydrocarbon fuel boiling in the range between about 75 F.and about 750 F. to which has been added from about 0.0025% to about0.05% by weight of a tetraalkyl ammonium salt of a C to C unsubstitutedaliphatic hydroxy carboxylic acid, the alkyl groups of said salt eachcontaining from 1 to about 24 carbon atoms.

5. A fuel as defined by claim 4 wherein said salt is a References Citedin the file of this patent UNITED STATES PATENTS 2,113,606 Taub et a1.Apr. 12, 1938 2,288,413 Morgan June 30, 1942 2,295,773 Chenicek Sept.15, 1942

1. A HYDROCARBON-OIL BOILING IN THE RANGE BETWEEN ABOUT 75*F. AND ABOUT750*F. HAVING INCORPORATED THEREIN FROM ABOUT 0.00005% TO ABOUT 0.5% BYWEIGHT OF A TETRAALKYL AMMONIUM SALT OF A C2 TO C10 UNSUBSTITUTEDHYDROXY CARBOXYLIC ACID, THE ALKYL GROUPS OF SAID SALT EACH CONTAININGFROM 1 TO ABOUT 24 CARBON ATOMS.